Polyetherimides are a family of thermoplastic resin compositions with important uses. Their preparation from arylene ether dianhydrides and diamines is described in Heath and Wirth, U.S. Pat. No. 3,847,867. Such materials modified by way of partially substituting dianhydrides of other types, e.g., pyromellitic-, diphenylsulfone- and benzophenone-dianhydrides, is also known from Williams III et al., U.S. Pat. No. 3,983,093. These modifications are reported to improve solvent resistance, thereby increasing the value of the resins in a wide variety of uses, including films, molding compounds and coatings. In any event, however, all such polyimides tend to have low solubility in halogenated solvents. There is a need to provide polyetherimide resin coating compositions with higher solids content in halogenated solvents. In addition, it would be desirable to enhance heat resistance as measured by thermal analysis and reported as glass transition temperature, Tg. It is also known to form polyimides, which are not polyetherimides, by reacting a fluorine analog of aromatic tetracarboxylic dianhydrides with diamines: Angelo, U.S. Pat. No. 3,424,718. In such polymers, pyromellitic dianhydride is replaced in part by fluoro-containing dianhydride, but there is no hint or suggestion that any such substitution into polyetherimides will enhance the solubility of the latter, especially in halogenated hydrocarbons, or elevate their Tg's.
It has now been surprisingly discovered, and is the subject matter of this invention, that the fluorocontaining dianhydride can replace a significant part of the bis ether anhydride in polyetherimides of the prior art and improve heat resistance. It is further surprisingly found that solubility in halogenated solvents is enhanced. Such copolymers have numerous uses as will be shown, with special utility in the field of coatings by deposition from solids.